Commit 10a70da7 authored by Emilia Kasper's avatar Emilia Kasper
Browse files

client: reject handshakes with DH parameters < 768 bits. 



Since the client has no way of communicating her supported parameter
range to the server, connections to servers that choose weak DH will
simply fail.

Reviewed-by: default avatarKurt Roeckx <kurt@openssl.org>
parent dcbc03ed

CHANGES

+2 −1
Original line number Diff line number Diff line
@@ -4,7 +4,8 @@ 


 Changes between 1.0.2a and 1.0.2b [xx XXX xxxx]



  *)

  *) Reject DH handshakes with parameters shorter than 768 bits.

     [Kurt Roeckx and Emilia Kasper]



 Changes between 1.0.2 and 1.0.2a [19 Mar 2015]

ssl/s3_clnt.c

+50 −23
Original line number Diff line number Diff line
@@ -2361,6 +2361,25 @@ int ssl3_get_server_done(SSL *s) 
    return (ret);

}



#ifndef OPENSSL_NO_DH

static DH *get_server_static_dh_key(SESS_CERT *scert)

{

    DH *dh_srvr = NULL;

    EVP_PKEY *spkey = NULL;

    int idx = scert->peer_cert_type;



    if (idx >= 0)

        spkey = X509_get_pubkey(scert->peer_pkeys[idx].x509);

    if (spkey) {

        dh_srvr = EVP_PKEY_get1_DH(spkey);

        EVP_PKEY_free(spkey);

    }

    if (dh_srvr == NULL)

        SSLerr(SSL_F_GET_SERVER_STATIC_DH_KEY, ERR_R_INTERNAL_ERROR);

    return dh_srvr;

}

#endif



int ssl3_send_client_key_exchange(SSL *s)

{

    unsigned char *p;
@@ -2603,25 +2622,14 @@ int ssl3_send_client_key_exchange(SSL *s) 
                goto err;

            }



            if (scert->peer_dh_tmp != NULL)

            if (scert->peer_dh_tmp != NULL) {

                dh_srvr = scert->peer_dh_tmp;

            else {

                /* we get them from the cert */

                int idx = scert->peer_cert_type;

                EVP_PKEY *spkey = NULL;

                dh_srvr = NULL;

                if (idx >= 0)

                    spkey = X509_get_pubkey(scert->peer_pkeys[idx].x509);

                if (spkey) {

                    dh_srvr = EVP_PKEY_get1_DH(spkey);

                    EVP_PKEY_free(spkey);

                }

                if (dh_srvr == NULL) {

                    SSLerr(SSL_F_SSL3_SEND_CLIENT_KEY_EXCHANGE,

                           ERR_R_INTERNAL_ERROR);

            } else {

                dh_srvr = get_server_static_dh_key(scert);

                if (dh_srvr == NULL)

                    goto err;

            }

            }



            if (s->s3->flags & TLS1_FLAGS_SKIP_CERT_VERIFY) {

                /* Use client certificate key */

                EVP_PKEY *clkey = s->cert->key->privatekey;
@@ -3464,25 +3472,44 @@ int ssl3_check_cert_and_algorithm(SSL *s) 
    }

#endif

#ifndef OPENSSL_NO_DH

    if ((alg_k & SSL_kEDH) &&

        !(has_bits(i, EVP_PK_DH | EVP_PKT_EXCH) || (dh != NULL))) {

        SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM, SSL_R_MISSING_DH_KEY);

    if ((alg_k & SSL_kEDH) && dh == NULL) {

        SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM, ERR_R_INTERNAL_ERROR);

        goto f_err;

    } else if ((alg_k & SSL_kDHr) && !SSL_USE_SIGALGS(s) &&

    }

    if ((alg_k & SSL_kDHr) && !SSL_USE_SIGALGS(s) &&

               !has_bits(i, EVP_PK_DH | EVP_PKS_RSA)) {

        SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM,

               SSL_R_MISSING_DH_RSA_CERT);

        goto f_err;

    }

# ifndef OPENSSL_NO_DSA

    else if ((alg_k & SSL_kDHd) && !SSL_USE_SIGALGS(s) &&

    if ((alg_k & SSL_kDHd) && !SSL_USE_SIGALGS(s) &&

        !has_bits(i, EVP_PK_DH | EVP_PKS_DSA)) {

        SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM,

               SSL_R_MISSING_DH_DSA_CERT);

        goto f_err;

    }

# endif

#endif



    if (alg_k & (SSL_kDHE | SSL_kDHr | SSL_kDHd)) {

        int dh_size;

        if (alg_k & SSL_kDHE) {

            dh_size = BN_num_bits(dh->p);

        } else {

            DH *dh_srvr = get_server_static_dh_key(sc);

            if (dh_srvr == NULL)

                goto f_err;

            dh_size = BN_num_bits(dh_srvr->p);

            DH_free(dh_srvr);

        }



        if ((!SSL_C_IS_EXPORT(s->s3->tmp.new_cipher) && dh_size < 768)

            || (SSL_C_IS_EXPORT(s->s3->tmp.new_cipher) && dh_size < 512)) {

            SSLerr(SSL_F_SSL3_CHECK_CERT_AND_ALGORITHM, SSL_R_DH_KEY_TOO_SMALL);

            goto f_err;

        }

    }

#endif  /* !OPENSSL_NO_DH */



    if (SSL_C_IS_EXPORT(s->s3->tmp.new_cipher) && !has_bits(i, EVP_PKT_EXP)) {

#ifndef OPENSSL_NO_RSA

ssl/ssl.h

+2 −0
Original line number Diff line number Diff line
@@ -2641,6 +2641,7 @@ void ERR_load_SSL_strings(void); 
# define SSL_F_GET_CLIENT_MASTER_KEY                      107

# define SSL_F_GET_SERVER_FINISHED                        108

# define SSL_F_GET_SERVER_HELLO                           109

# define SSL_F_GET_SERVER_STATIC_DH_KEY                   340

# define SSL_F_GET_SERVER_VERIFY                          110

# define SSL_F_I2D_SSL_SESSION                            111

# define SSL_F_READ_N                                     112
@@ -2906,6 +2907,7 @@ void ERR_load_SSL_strings(void); 
# define SSL_R_DATA_LENGTH_TOO_LONG                       146

# define SSL_R_DECRYPTION_FAILED                          147

# define SSL_R_DECRYPTION_FAILED_OR_BAD_RECORD_MAC        281

# define SSL_R_DH_KEY_TOO_SMALL                           372

# define SSL_R_DH_PUBLIC_VALUE_LENGTH_IS_WRONG            148

# define SSL_R_DIGEST_CHECK_FAILED                        149

# define SSL_R_DTLS_MESSAGE_TOO_BIG                       334

ssl/ssl_err.c

+3 −1
Original line number Diff line number Diff line 
/* ssl/ssl_err.c */

/* ====================================================================

 * Copyright (c) 1999-2014 The OpenSSL Project.  All rights reserved.

 * Copyright (c) 1999-2015 The OpenSSL Project.  All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions
@@ -119,6 +119,7 @@ static ERR_STRING_DATA SSL_str_functs[] = { 
    {ERR_FUNC(SSL_F_GET_CLIENT_MASTER_KEY), "GET_CLIENT_MASTER_KEY"},

    {ERR_FUNC(SSL_F_GET_SERVER_FINISHED), "GET_SERVER_FINISHED"},

    {ERR_FUNC(SSL_F_GET_SERVER_HELLO), "GET_SERVER_HELLO"},

    {ERR_FUNC(SSL_F_GET_SERVER_STATIC_DH_KEY), "GET_SERVER_STATIC_DH_KEY"},

    {ERR_FUNC(SSL_F_GET_SERVER_VERIFY), "GET_SERVER_VERIFY"},

    {ERR_FUNC(SSL_F_I2D_SSL_SESSION), "i2d_SSL_SESSION"},

    {ERR_FUNC(SSL_F_READ_N), "READ_N"},
@@ -459,6 +460,7 @@ static ERR_STRING_DATA SSL_str_reasons[] = { 
    {ERR_REASON(SSL_R_DECRYPTION_FAILED), "decryption failed"},

    {ERR_REASON(SSL_R_DECRYPTION_FAILED_OR_BAD_RECORD_MAC),

     "decryption failed or bad record mac"},

    {ERR_REASON(SSL_R_DH_KEY_TOO_SMALL), "dh key too small"},

    {ERR_REASON(SSL_R_DH_PUBLIC_VALUE_LENGTH_IS_WRONG),

     "dh public value length is wrong"},

    {ERR_REASON(SSL_R_DIGEST_CHECK_FAILED), "digest check failed"},